{{short description|Flag with a V-shaped cut}} {{More citations needed|date=November 2025}}
{{multiple images |direction = vertical |image1 = Flag_shape_swallowtail.svg |caption1 = Swallowtail flag shape |image2 = 800px-hirundorusticaflightcropped.jpg |caption2 = A barn swallow in flight. Note the shape of its tail }}
In flag terminology, a '''swallowtail''' is either # a V-shaped cut in a flag that causes the flag to end in two points at the fly; or # any flag that has this V-shaped cut. The name comes from the forked tail that is a common feature of the swallow species of birds.
{{Gallery |title= |mode=nolines|style=background:var(--background-color-neutral, beige); color:var(--color-base, black); padding:20px|whitebg=no|height=110|width=230|align=left |File:Alpha.svg|Alfa flag (nautical signal flag for "A") |File:Naval Ensign of Poland.svg|Naval ensign of Poland |File:Naval Ensign of Germany.svg|Naval ensign of Germany |File:Flag of Vietnamese Pure Land Buddhist Laity Association.svg|Flag of the Vietnamese Pure Land Buddhist Laity Association|Socony House Flag.gif|House flag of Socony-Vacuum Oil Company}} {{clear}}
A swallowtail can also be used to easily deface an existing flag as seen following World War II to both follow international maritime law that dictates a flagged vessel must fly the flag of registration from its stern, but that its use immediately following a war could suggest that the ship is unaware of the surrender or still under orders of the belligerent government.<ref name="NOAA">{{cite web |title=Jurisdiction Over Vessels |url=https://www.noaa.gov/jurisdiction-over-vessels |website=noaa.org |publisher=National Oceanic and Atmospheric Administration |date=23 July 2025}}</ref>
As such, the Allied Control Council in Europe dictated that ''"every German or ex-German vessel operating under the Allied Control Authority shall at all times wear the Allied Control Authority distinguishing flag which shall consist of International Flag "C" with a triangle cut from the fly."'', and Supreme Commander for the Allied Powers in Japan dictated Japanese vessels carry an "D" flag to acknowledge they had accepted Allied occupational authority.<ref>{{cite web |last1=Ytrup |first1=Kenny |title=C-Doppelstander – German occupation ensign |url=https://www.flaggeek.net/p/c-doppelstander-german-occupation-ensign.html |website=flaggeek.net |date=14 March 2026}}</ref><ref>{{cite journal |title=Law No. 39 |journal=Enactments and Approved Papers of the Control Council and Coordinating Committee, Allied Control Authority, Germany |date=1945–1948 |volume=V |page=153 |url=https://www.loc.gov/item/61035888_Volume-V/ |publisher=Control Council And Coordinating Committee Of The Allied Control Authority |location=U.S. Library of Congress}}</ref>
{{Gallery |title= |mode=nolines|style=background:var(--background-color-neutral, beige); color:var(--color-base, black); padding:20px|whitebg=no|height=110|width=230|align=left |File:Merchant flag of Germany (1946–1949).svg|"C-Pennant" (C-Doppelstander) as used during the occupation of Germany |File:Flag of Allied Occupied Japan.svg|Swallowtailed "D" ensign used during the occupation of Japan}} {{clear}}
==Variants== ===Double-pointed=== Common in the Nordic countries, this swallowtail flag contains a vertical section in the centre of the fly.
{{Gallery |title= |mode=nolines|style=background:var(--background-color-neutral, beige); color:var(--color-base, black); padding:20px|whitebg=no|height=110|width=230|align=left |File:Naval Ensign of Denmark.svg|Naval ensign of Denmark |Flag of Iceland (state).svg|State flag of Iceland |File:Flag of the President of Iceland.svg|Presidential standard of Iceland }} {{clear}}
===Swallowtail with tongue=== Also common in the Nordic countries, the swallowtail flag contains a third tail (the "tongue") between the other two tails.
{{Gallery |title= |mode=nolines|style=background:var(--background-color-neutral, beige); color:var(--color-base, black); padding:20px|whitebg=no|height=110|width=230|align=left |File:Naval Ensign of Sweden.svg|Naval ensign of Sweden |File:Flag of Norway, state.svg|State flag of Norway |File:Military Flag of Finland.svg|Naval ensign of Finland |File:Naval Ensign of Estonia.svg|Naval ensign of Estonia }} {{clear}}
===Triangular swallowtail=== The triangular swallowtail is the shape of the flag of the American state of Ohio,<ref>{{cite web |last1=Scullin |first1=Katy |title=A Swallowtail What? The History of Ohio's State Flag |url=https://ohiomemory.ohiohistory.org/archives/6169 |website=Ohio Memory |publisher=Ohio History Connection |date=17 May 2024}}</ref> as well as of some burgees, private signals and pennants of the International Code of Signals (ICS).
{{Gallery |title= |mode=nolines|style=background:var(--background-color-neutral, beige); color:var(--color-base, black); padding:20px|whitebg=no|height=110|align=left |File:Flag of Ohio.svg|State flag of Ohio |File:Burgee of detroityc.svg|Burgee of the Detroit Yacht Club |File:ICS Group.svg|International signal flag for "group" }} {{clear}}
===Guidon=== A guidon is the general name given to a small swallowtail flag. Guidons are used to represent military units and are displayed on vehicles attached to a particular unit. In some countries (such as the United States), guidons do not necessarily have a swallow tail.
The military use of the guidon originated from the flags used by cavalry units in Europe. A variant of the guidon, the hussar cut, was used by German cavalry regiments. Instead of a straight V-shaped cut, the swallowtail in a hussar cut flag is curved.
{{Gallery |title= |mode=nolines|style=background:var(--background-color-neutral, beige); color:var(--color-base, black); padding:20px|whitebg=no|height=110|align=left |File:US Cav 35.svg|Guidon of the USA 7th Cavalry Regiment (19th century) |File:Prussian standard.jpg|Prussian cavalry standard with hussar cut (18th century) }} {{clear}}
== References == {{Reflist}}
{{Vexillology}}
Category:Types of flags